This invention relates to a thermal switch and, more particularly, to a thermal switch with integrated over protection circuitry.
Heating elements, such as cartridge heaters, are used for various applications, including heating of liquids. Typically, the heater is wired in a control circuit that regulates operation of the heater to maintain a desired temperature. This may be done with a separate temperature or thermal switch.
A thermal switch, such as a thermostat, has a control contact wired in series with the heater to control operation of the heater. The thermostat could be mounted to a vessel holding the liquid. Alternatively, the thermostat could be submerged in the liquid. However, such a thermostat and heater are not protected against malfunction such as high current surges, electrical shorts and overheating of the liquid caused by the heater.
The present invention is directed to improvements in thermal switch assemblies.
In accordance with the invention there is provided a thermal switch including an integral control circuit.
Broadly, there is disclosed herein a thermal switch comprising an elongate tubular sealed housing. A control circuit is mounted in the sealed housing. The control circuit comprises a thermostat, a fuse and a thermal overload switch electrically connected in series. An electrical connector is mounted to the housing and is connected to the control circuit.
It is a feature of the invention that the housing comprises a metal bushing housing the thermostat and the thermal overload switch. A flexible tube is secured to the metal bushing. The bushing and the flexible are filled with epoxy.
In accordance with one aspect of the invention, a heater is connected to the housing and wired in series in the control circuit. The heater may comprise a cartridge heater brazed to a metal bushing of the housing. The cartridge heater is filled with magnesium oxide.
In accordance with another aspect of the invention, a sealed thermal switch is provided for controlling liquid temperature. The switch comprises an elongate tubular submersible sealed housing. A control circuit mounted in the housing comprises a thermostat, a fuse and a thermal overload switch electrically connected in series. An electrical connector is sealed to the housing and connected to the control circuit.
Further features and advantages of the invention will be readily apparent from the specification and from the drawings.